JPS6223496B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention aims to prevent trouble from occurring when switching from FM mode to AM mode in an FM-AM receiver.

Let's explain one example below.

In FIG. 1, 10 indicates an FM receiving section, and 1
1 is the antenna tuning circuit, 12 is a high frequency amplifier, 13 is an interstage tuning circuit, 14 is a mixer circuit, 1
5 is a local oscillation circuit, and 16 is its resonance circuit.
When receiving FM, the function switch (band switching switch) 36 is switched to the FM side contact F as shown in the figure, and the power terminal 39 is switched to the FM side contact F as shown in the figure.
through switch 36 to circuit 12,
14 and 15 as their operating voltage, and, although not shown, the operating voltage is always supplied to the circuits in the next stage and subsequent stages regardless of the switching of the switch 36.

Therefore, from the mixer circuit 14, the received FM
An intermediate frequency signal of the wave is taken out, and this intermediate frequency signal is passed through a bandpass filter 17 having, for example, an intermediate frequency transformer and a ceramic filter.
The demodulated signal is further supplied to the FM demodulation circuit 19 through the limiter amplifier 18 for intermediate frequency amplification and demodulated, and the demodulated signal is sent to the attenuator 21 for level adjustment → the FM side contact F of the function switch 31 → for muting, which will be described later. is supplied to the stereo demodulation circuit 33 through the switch circuit 32, and when the demodulated signal is a stereo composite signal,
The left and right channel stereo signals are demodulated from the stereo composite signal, which is sent to the output terminal 34.
On the other hand, when the demodulated signal is a monaural signal, the monaural signal is
It is taken out as it is to the terminals 34L and 34R.

Further, 40 indicates an AM receiving section, 41 an antenna tuning circuit thereof, 42 a mixer circuit, 43 a local oscillation circuit, and 44 a resonance circuit thereof. and,
When receiving AM, the switch 36 switches to AM, contrary to the diagram.
The side contact A is switched, and the voltage from the terminal 39 is supplied to the circuits 42 and 43 as their operating voltage, and the operating voltage is always supplied to the circuits from the next stage onwards regardless of the switching of the switch 36.

Therefore, from the mixer circuit 42, the received AM
An intermediate frequency signal of the wave is taken out, and this intermediate frequency signal is passed through a bandpass filter 45 having, for example, an intermediate frequency transformer and a ceramic filter.
is further supplied to the detection circuit 47 through the amplifier 46 for intermediate frequency amplification and detected, and the detected signal is sent to the attenuator 48 for level adjustment → the AM side contact A of the switch 31 → the switch circuit 32 →
Through the stereo demodulation circuit 33, the terminals 34L, 34
It is taken out by R.

Also, at this time, the detection signal from the detection circuit 47 is supplied to the low-pass filter 51 to extract the DC component, that is, the AGC voltage at a level corresponding to the input electric field level. ) 52 to the mixer circuit 42
and is supplied to an intermediate frequency amplifier 46 to perform AGC.

Such FM receiving section 10 and AM receiving section 40
In contrast, the muting circuit is configured as follows.

That is, during FM reception, the FM intermediate frequency signal obtained by the intermediate frequency amplifier 18 is supplied to the detection circuit 23 and detected, and this detected signal is supplied to the low-pass filter 24 to output the signal at a level corresponding to the input electric field level, and , a DC voltage whose level changes in accordance with the bandwidth, that is, a muting signal is formed, and this muting signal is supplied to an adder circuit (combining circuit) 65 through a switch circuit 25.

Further, during AM reception, the detection signal obtained by the detection circuit 47 is supplied to the low-pass filter 54 to form a muting signal, and this muting signal is passed through the switch circuit 55 to the addition circuit 65.
supplied to

Then, the output signal of the adder circuit 65 is supplied to the switch circuit 32 as its control signal through an attenuator 64 for setting a muting level, a muting switch 66, and a Schmitt circuit 67.

Furthermore, the presence or absence of voltage at contact A of the switch 36 is detected by the detection circuit 61, and the detection signal is supplied to the switch circuits 25 and 55 as a control signal. ), the switch circuit 25 is turned on and the switch circuit 55 is turned off, as shown in the figure.
When receiving AM (when voltage is being supplied to contact A), the switch circuit 25 is turned off and the switch circuit 55 is turned on, contrary to the diagram.

Further, the input electric field level display circuit is configured as follows.

That is, the DC voltage from the filter 24 passes through the switch circuit 28 to the adder circuit (combining circuit) 6.
8. Further, the DC voltage from the filter 54 is supplied to the adder circuit 68 through the switch circuit 58. The output signal of the adder circuit 68 is then supplied to an input level meter 69.

Further, the detection signal from the detection circuit 61 is supplied to the switch circuits 28 and 58 as their control signals, and the switch circuits 28 and 58
It is controlled in the same way as 5 and 55.

Furthermore, in order to ensure the operation of the muting circuit and the input electric field level display circuit, the following configuration is provided.

That is, the contact A of the switch 36 is connected to the resistor 7.
1 is connected to, for example, a bias circuit of an amplification transistor of the intermediate frequency amplifier 18.

Further, the DC power supply 73 is connected to the adder circuit 52 through a switch circuit 74, and the detection signal of the detection circuit 61 is supplied to the switch circuit 74 as its control signal.
It is turned on as shown in the figure when receiving, and turned off when receiving AM.

In addition, the part surrounded by the chain line in the figure is one IC.
Converted to IC.

According to such a configuration, the switches 31, 36
is switched to contact F, the mode is FM broadcast reception mode, but at this time, the detection circuit 6
The switch circuits 25, 55,
28, 58, and 74 are switched to the state shown in the figure.
Therefore, the muting signal from the filter 24 is supplied to the switch circuit 32 through the switch circuit 25, the adder circuit 65, the attenuator 64, the switch 66, and the simulating circuit 67, and muting is performed when receiving FM.

Also, at this time, a voltage indicating the input electric field level from the filter 24 is supplied to the meter 69 via the switch circuit 28→addition circuit 68, and the input electric field level of the FM wave is displayed.

When receiving this FM, the DC voltage from the power supply 73 is applied to the mixer circuit 42 and intermediate frequency amplifier 46 via the switch circuit 74 → the adder circuit 52.
Since it is supplied as AGC voltage, these circuits 4
The gains of the switch circuits 55, 58 are lowered, the detection circuit 47 cannot obtain a detection signal, and the switch circuits 55, 58
is also off. Therefore, the muting operation and the display of the input electric field level during FM reception are not influenced by the AM receiving section 40.

On the other hand, when the switches 31 and 36 are switched to the contact A, the AM broadcast reception mode is entered. can be switched to the opposite state. Therefore, filter 5
The muting signal from 4 is sent to the switch circuit 5.
The signal is supplied to the switch circuit 32 through 5→adder circuit 65→attenuator 64→switch 66→schmitt circuit 67, and muting is performed during AM reception.

Also, at this time, a voltage indicating the input electric field level from the filter 54 is supplied to the meter 69 via the switch circuit 58→addition circuit 68, and the input electric field level of the AM wave is displayed.

During AM reception, the DC voltage at the terminal 39 is supplied to the bias circuit of the intermediate frequency amplifier 18 through the contact A of the switch 36 and the resistor 71, which shifts the bias of the intermediate frequency amplification transistor and amplifies it. operation is stopped,
No detection signal is obtained in the detection circuit 23, and the switch circuits 25 and 28 are also off. Therefore AM
The muting operation during reception and the display of the input electric field level are not affected by the FM receiving section 10.

Thus, according to the invention, in particular the DC power supply 7
3 and a switch circuit 74, the FM
No trouble occurs when switching from mode to AM mode. That is, the DC power supply 73
And if the switch circuit 74 is not provided, the FM
During reception, the AGC voltage from the filter 51 cannot be obtained and therefore the intermediate frequency amplifier 46 is at maximum gain, so when switching from FM mode to AM mode next time, the intermediate frequency amplifier 46 outputs an intermediate signal at the maximum level. A frequency signal is extracted, and therefore a loud sound is suddenly emitted from a speaker (not shown), which may damage the speaker or startle the listener. Alternatively, the muting may malfunction or the meter 69 may go overboard.

However, according to the present invention, since the DC power supply 73 and the switch circuit 74 are provided to reduce the gain of the intermediate frequency amplifier 46 during FM reception, the following
When switching from FM mode to AM mode, the level of the intermediate frequency signal from the intermediate frequency amplifier 46 gradually increases, so that a sudden loud sound does not damage the speaker or startle the listener. Alternatively, the next time the mode is switched from FM mode to AM mode, the muting will not malfunction or the meter 69 will not swing out.

Furthermore, during FM reception, the voltage from the power supply 73 lowers the gains of the mixer circuit 42 and the intermediate frequency amplifier 46, making it impossible to obtain a detection signal from the detection circuit 47, so that a muting signal (DC voltage) from the filter 54 is also obtained. Therefore, even if the switch circuit 55 is not provided, muting should be performed at the time of FM reception.

However, since the filter 54 must extract only the DC component that is not included in the output signal of the detection circuit 47, its time constant must be sufficiently large. Therefore, switches 31 and 36
Even when switching from AM mode to FM mode, a DC voltage, that is, a muting signal, is still obtained from the filter 54 for a short time after the switch.

Therefore, if the switch circuit 55 is not provided, when the switches 31 and 36 are switched to the FM mode, the muting signal from the filter 54 is supplied to the switch circuit 32 through the adder circuit 65, turning it on. Therefore, when switches 31 and 36 are switched to FM mode,
Muting is canceled, so at this time,
If the FM is out of tune, or even if it is in tune, the input electric field level is too small to release the muting, and the muting will be released and the noise will be transmitted to the terminals 34L, 34L,
34R, causing discomfort to the listener.

Similarly, if the switch circuit 58 is not provided, when the switches 31 and 36 are switched to FM mode, the DC voltage remaining in the filter 54 is added to the DC voltage from the filter 24. The meter 69 may go overboard.

However, in the above receiver, switch circuits 55 and 58 are provided, and switches 31 and 36 are
When switching to the mode, the DC voltage remaining in the filter 54 is cut off, so there is no possibility of noise caused by muting malfunction or the meter 6
9 never gets shaken off.

Note that since the output signal of the detection circuit 23 does not include an AM component, the time constant of the filter 24 is small, so when the filters 31 and 36 are switched to AM mode, almost no DC voltage remains in the filter 24. Since there are no switch circuits, the switch circuits 25 and 28 may not be provided, but if they are provided, it will be even more effective.

Figure 2 shows an example of the connection of the main parts.
_The emitters of _{Q 11 and} Q ₁₂ are connected to _a constant current source Transistors Q ₁₅ and Q ₁₆ are differentially connected using Q ₁₂ as a constant current source. Transistors Q ₃₁ and Q ₃₅ forming a current mirror circuit 82 are connected to the collectors of the transistors Q ₁₄ and Q ₁₆ as loads. In addition,
Transistor Q ₃₃ is for biasing transistors Q ₃₁ and Q ₃₂ .

In this case, transistors Q ₁₄ and Q ₁₆ correspond to switch circuits 55, 58, and 74, and there is no transistor corresponding to switch circuits 25 and 28. Further, 83 to 87 are current mirror circuits, respectively.

Then, during AM reception, the voltage at terminal 39 is
The contact A of the switch 36 is supplied to the bases of the transistors Q ₁₄ and Q ₁₆ through the resistor 77, and the transistors Q ₁₄ and Q ₁₆ are turned on.
Q ₁₃ and Q ₁₅ are turned off. Therefore, transistors Q ₂₁ and Q ₂₂ of current mirror circuit 83 are turned off, and thereby transistor Q ₁ is also turned off.

Then, the DC voltage from the filter 54 is supplied to the transistor _Q12 to be converted into a current, and
The current is amplified by the differential amplifier 81, and the output current is passed through the cant mirror circuit 82 → the transistor Q ₄₁ of the current mirror circuit 84 (transistor Q ₄₄ is for bias) → the same transistor Q ₄₃ → the transistor Q ₇₁ of the current mirror circuit 87, It is supplied to the variable resistor 64 through Q ₇₂ and converted into voltage.
This voltage is supplied to the switch circuit 32 through the muting switch 66 and the Schmitt circuit 67, and muting is performed during AM reception.

Further, the output current of the differential amplifier 81 is supplied to the meter 69 through the current mirror circuit 82 → the transistor Q ₄₁ of the current mirror circuit 84 → the transistor Q ₄₂ → the transistors Q ₆₂ and Q ₆₁ of the current mirror circuit 86, and the AM wave The input electric field level is displayed.

On the other hand, when receiving FM, the switch 36 is switched to contact F, contrary to the diagram, so the transistor
Q ₁₄ and Q ₁₆ are turned off, and transistors Q ₁₃ and Q ₁₅
is turned on. Therefore, transistors Q ₂₁ , Q ₂₂
is turned on, and a predetermined DC voltage is obtained at the emitter of the transistor Q ₁ by the constant voltage diode D ₁ , which constitutes a power supply 73 , and this DC voltage is applied to the mixer circuit 42 and the summing resistor 52 . It is supplied as an AGC voltage to intermediate frequency amplifiers 46 and their gains are reduced.

Also, at this time, the transistors Q ₁₄ and Q ₁₆ are turned off, so even if there is a DC voltage remaining in the filter 54, it is not supplied to the current mirror circuit 82, so that the remaining DC voltage is , is not supplied to the switch circuit 18 or the meter 69.

Then, the DC voltage from the filter 24 is supplied to the transistor Q ₃ for current amplification, and the output current is transmitted to the variable resistor 64 through the transistor Q ₅₁ of the current mirror circuit 85 → the transistor Q ₅₃ → the current mirror circuit 87. supplied,
Therefore, muting is performed when receiving FM.

Further, the output current of the transistor Q ₃ is supplied to the meter 69 through the transistor Q ₅₁ of the current mirror circuit 85 → the transistor Q ₅₂ → the current mirror circuit 86, and the input electric field level of the FM wave is displayed.

In the above description, for the purpose of explanation, the switch circuit 3
2 is provided separately, but this is a stereo demodulation circuit 33
The switching element for switching demodulation may also be used. Also, the demodulation circuit 33 and the terminal 3
A similar switching circuit may be provided between 4L and 34R. Further, the inputs of the filters 24 and 54 may have information regarding the bandwidth of the intermediate frequency stage of the receiving sections 40 and 10 or the input electric field level. Further, an adder circuit may be used in place of the switch 31, and the switch 66 may be omitted.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of an example of the present invention, and FIG. 2 is a connection diagram of a part thereof. 10 is an FM receiving section, 40 is an AM receiving section, and 33 is a stereo demodulation circuit.

Claims (1)

[Claims] 1 When receiving FM, at least turn off the power line of the mixer circuit for AM, and when receiving AM,
In an FM-AM receiver that selectively receives FM broadcasts and AM broadcasts by turning off at least the power line of the mixer circuit for FM, the above-mentioned FM
An FM-AM receiver that reduces the gain of the AM intermediate frequency amplifier by supplying a predetermined bias voltage to the AM AGC voltage line during reception.